1. Field of the Invention
The present invention relates to a camera for getting information upon three-dimensional shape.
2. Description of the Related Arts
For example, as a method for getting information upon three-dimensional shape, there has conventionally been proposed a method for getting the information from a pair of images that have passed through a plurality of photographing lenses, and there has conventionally been proposed a method for detecting distance distribution by projecting light onto an object (or subject) on the basis of the principle of triangulation, as shown in FIG. 23.
Also, for example, there has been proposed a method for detecting distance distribution by projecting a fringe pattern onto an object and by inputting the fringe pattern by another camera, on the basis of the principle of triangulation, as disclosed in Japanese Laid-Open Patent Publication No. 6-249624.
Also, for example, there has conventionally been proposed a method to seek for an undulation (or up and down) of an object by projecting a lattice pattern onto the object and by observing the object in different angles, in which modified data corresponding to the modified lattice pattern formed in compliance with the undulation of the object is gained (Journal of the Institute of Precision Engineering, 55, 10, 85 (1989)).
Also, for example, there has conventionally been proposed a method for measuring optical distribution by projecting a gray-code pattern with a CCD camera, instead of projecting the lattice pattern, as shown in FIG. 24.
In order to gain the information upon the three-dimensional shape with the aforementioned method, however, there is need of taking (or photographing) a plurality of images, and the process, subsequent to taking the images, of the information is complex. As a result, a longer time is required for an operation to take an image of the object, and/or a longer time is required for processing the information after taking the image. In other words, it is considered that there is no special problem if the aforementioned method is employed for any measuring device; however, it is considered that it is not suitable to apply the method to any camera.
Therefore, as a method for speedily getting the information upon three-dimensional shape with higher precision, for example, there has been proposed the following method therefor.
Namely, as shown in FIG. 25 (Source: “Optical Three-Dimensional Measurement,” edited by Toru Yoshizawa, Shin-Gijutsu Communications (or New Technical Communications), page 89, FIGS. 5.2.12a), a stripe pattern is firstly projected onto an object (or subject) to be photographed; and the stripe pattern formed on the object is detected at an angle determined in terms of a design relative to the projected stripe pattern; and then the distance distribution of the object is detected from the deformed image of the stripe pattern in compliance with the unevenness (or irregularity) of the object. That is, with respect to a phase of an image measured at each image point, a shift (or swerve, or change) in phase relative to its original stripe is computed. The phase shift includes information upon the height of the object. In this relation, the distance distribution of the object is sought, or determined, from the phase information and its triangulation information. However, there is need of high precision for the detection. Because there is a limitation in density distribution of the stripe pattern or in light intensity thereof, there has been employed a method for seeking the distance distribution of the object by a plurality of images taken with the position of the stripe pattern being shifted bit by bit. Based upon this method, for example, stripe patterns with four shifts in phase of 0°, 90°, 180° and 270°, are projected. By the way, as a measuring device, there has been conventionally provided a commercial product in which a slitting light is scanned. According to the measuring device, it takes several hundreds of milliseconds to scan the slitting light for the purpose of getting the information upon three-dimensional shape information. Meanwhile, there has conventionally been provided a digital camera in which a plurality of images are consecutively taken in case that the photographing mode is a successively photographing mode and in which the image is recorded (or stored) upon a memory card after the plurality of images are taken (or after the object is successively photographed); however, the digital camera is not a camera for getting information upon three-dimensional shape.
According to the aforementioned method, however, if the stripe pattern which has a plurality of sub-stripes has only one cycle, the density distribution becomes so rough that it is not possible to heighten the precision for getting the information upon three-dimensional shape.
In order to solve this technical problem, there have conventionally been taken measures in which stripe patterns with several cycles are projected onto the object. In this case, however, if the object has a deep distance distribution, it is not possible to identify a particular piece of information upon which particular sub-stripe of the stripe pattern the particular piece of information corresponds to. Namely, in this case, the angle used in the triangulation may be interpreted as a different angle, depending upon a situation in which the particular sub-stripe of the stripe pattern falls upon a particular ordinal number of the plurality of sub-stripes. As a result, a wrong distance distribution is gained.
More specifically, for example, as shown in FIG. 28, a point “A” which is on a fore plane “P1” becomes a piece of information upon the third stripe; on the other hand, a point “B” which is on a rear plane “P2” becomes another piece of information upon the fourth stripe. However, if it is not possible to identify which ordinal number of sub-stripe the particular plane corresponds to, the points “A” and “B” can not be distinguished from each other, only on the basis of information upon the image sensed by its light receiving part.
Furthermore, in case of increasing the number of points for detection by increasing the number of sub-stripes in a particular stripe pattern for the purpose of enhancing the precision in distance distribution, if a particular sub-stripe is wrongly identified in which ordinal number of sub-stripes it corresponds to, there increases the possibility to falsely detect the information upon the three-dimensional shape of the object.
Under the circumstance, for the purpose of reducing such a misdetection of the information thereupon, and for the purpose of increasing the accuracy for identifying any particular sub-stripe of the stripe pattern, applicant has proposed the following improvement of the stripe pattern to be projected (see, for example, Japanese Patent Application No. 11-87124, not laid open yet).
That is, according to the improvement, for example, a pattern having a plurality of frequencies, and/or a pattern having a plurality of codes and stripes, and/or a light having a colored pattern is/are projected onto an object. Further, according to the improvement, not only such a pattern with a gradation, but also a marker to be able to identify a particular position or location on the pattern, are projected onto the object.
Meanwhile, generally, image taking devices and apparatuses have monitors (or monitoring devices) for letting their users confirm an image of the object (or subject) which has been photographed.
If the monitor applies to the camera for getting information upon three-dimensional shape in which the stripe pattern as aforementioned, is projected onto an object, and if the monitor is kept on all the time so as to allow the user to monitor the image of the object any time, applicant has found the following problem.
Namely, if such a stripe pattern is projected onto the object, the image of the object displayed on the monitor of the camera often becomes an image which gives the user (or photographer) a feeling of unpleasantness, as shown in FIG. 25.
In other words, applicant has found that:    (1) In order to gain information upon three-dimensional shape with higher precision or accuracy, it is necessary, for example, to change a stripe pattern, and/or to increase the number of sub-stripes in the stripe pattern, and/or to make the stripe pattern complex, and/or to add a marker to the stripe pattern, and/or to add some color to the marker etc.    (2) However, as the stripe pattern is more and more improved in order to gain information upon three-dimensional shape with higher precision or accuracy, the image which is displayed on the monitor of the camera becomes complex in inverse proportion to such improvements, which in turn gives the user a feeling of unpleasantness.